We have used patch clamp techniques to study the enzymatic regulation of voltage-activated calcium channels in a rat pituitary tumor cell line. Previous work in this laboratory has established that these dihydropyridine-sensitive calcium channels only respond to depolarization when the protein(s) forming the channel are phosphorylated; in the absence of phosphorylation they are completely inactivated. Furthermore, the response to depolarization is specific to the kinase that acts on the channel: protein kinase C does not alter channel activity but the cAMP-dependent kinase produces short bursts of very brief openings and a calcium/calmodulin-dependent kinase produces long bursts of much longer openings. Two phosphatases have also been implicated in the regulation of these channels. The calcium/calmodulin-dependent phosphatase 2b, calcineurin, rapidly inactivates the channels when intracellular calcium concentration exceeds 1 (mu)M. In addition, recent studies with okadaic acid, the potent tumor promoter that is the major toxin in shellfish poisoning, have also implicated phosphatase 1 in calcium channel regulation. We are now beginning to characterize the role of these enzymes in calcium channel regulation dihydropyridines, compounds used clinically to treat stress-related human cardiovascular disease, and by hypothalamic neuropeptides that control pituitary hormone secretion. New evidence suggests that dihydropyridines produce their effects on these channels by altering their susceptibility to protein phosphorylation and its removal. In addition, we have shown that the GTP-dependent effects of neuropeptides reported widely in the literature do not result from direct interactions of GTP-binding proteins with the channels as suggested previously. Instead, the G proteins appear activate the kinases and phosphatases through conventional second messengers. These experiments are leading us to a molecular model of calcium channel function that will contribute to an understanding of the toxicity of environmental hazards.